Anaphylaxis is a Blood-typed offensive move.
It provokes an immunological reaction in the victim resulting in a rapid-onset allergic reaction. It causes an alarming drop in the victim's blood pressure and respiratory difficulties due to swelling (and, by proxy, usually some hypoxia), and in some species may result in a visible swelling, rash or cyanosis. It's always accompanied by abdominal pain and a headache; and often with dizziness resulting in disorientation.
Its accuracy is not notably increased by an immobilised victim, since it's not contact-based. Similarly, its accuracy cannot be boosted. It is, however, affected by evasive manoeuvres, which is to say it can be made less accurate.